Say a rogue is fighting an enemy, and either they or someone else has unseen servant and they sent it to engage that enemy. Can the rogue now use a Sneak Attack?
Unseen Servant is very clearly described as an entity that shouldn't be used or useful in combat, this seems to go against that idea. In the same vein, rogues get sneak attack when there are others supporting them, again, the idea of them (if multiclassing) using a spell for this seems to be more of a loophole than a valid strategy.
Jeremy Crawford weighed in on this with an unofficial tweet, saying that
Unseen servant creates "an invisible, mindless, shapeless force." In combat, it doesn't act as an enemy/ally.
The idea behind sneak attack being allowed with an ally that is adjacent to the enemy is that someone is distracting that enemy. In the case of the Unseen Servant, there's nothing to really distract the enemy since it's Invisible and doesn't really interact with them.
There is the possibility of distracting the enemy in other ways (like dropping a stack of plates), but it would be up to your DM whether that would grant advantage or a sufficient distraction to satisfy sneak attack.
From the official Sage Advice Compendium:
Can I use unseen servant to act as an ally when using a class feature like Sneak Attack?
Unseen servant creates “an invisible, mindless, shapeless force”. In combat, it doesn’t act as a creature, an enemy, or an ally.
